Complete BFS-1

Problem58.java

@@ -0,0 +1,25 @@
+// Time Complexity : O(N)
+// Space Complexity : O(h)
+
+class Solution {
+    private List<List<Integer>> result;
+    public List<List<Integer>> levelOrder(TreeNode root) {
+        this.result = new ArrayList<>();
+        helper(root, 0);
+        return result;
+    }
+
+    private void helper(TreeNode root, int level) {
+        //base
+        if(root == null) return;
+
+        //logic
+        if (this.result.size() == level) {
+            result.add(new ArrayList<>());
+        }
+        this.result.get(level).add(root.val);
+
+        helper(root.left, level+1);
+        helper(root.right, level+1);
+    }
+}

Problem59.java

@@ -0,0 +1,46 @@
+// Time Complexity : O(V+E)
+// Space Complexity : O(V+E)
+
+class Solution {
+    public boolean canFinish(int numCourses, int[][] prerequisites) {
+        int[] inDegrees = new int[numCourses];
+        Map<Integer, List<Integer>> coursesMap = new HashMap<>();
+
+        for (int[] prerequisit: prerequisites) {
+            // prerequisit[0] - dependent; prerequisit[1] - inDependent
+            inDegrees[prerequisit[0]]++;
+            coursesMap.putIfAbsent(prerequisit[1], new ArrayList<>());
+            coursesMap.get(prerequisit[1]).add(prerequisit[0]);
+        }
+
+        int count = 0;
+        Queue<Integer> q = new LinkedList<>();
+
+        for (int i = 0; i < numCourses; i++) {
+            if (inDegrees[i] == 0) {
+                q.offer(i);
+                count++;
+            }
+        }
+
+        if (q.isEmpty()) return false;
+        if (count == numCourses) return true;
+
+        while (!q.isEmpty()) {
+            int inDependentCourse = q.poll();
+            List<Integer> dependentCourses = coursesMap.get(inDependentCourse);
+            if (dependentCourses != null) {
+                for (int dependentCourse: dependentCourses) {
+                    inDegrees[dependentCourse]--;
+                    if (inDegrees[dependentCourse] == 0) {
+                        q.offer(dependentCourse);
+                        count++;
+                        if (count == numCourses) return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+}